Electric switching device



Aug. 25, 1936. H. o. SIEGMUND ELECTRIC SWITCHING DEVICE Filed May 1,1935 APPl/ED VOL TA 65 MUG 3 H 4 mm o 2 r H. M um m E m w T w J M //vVEN TOR H. 0. 5/5 GM UND A TTOP V Patented A6 25,1936

PATENT OFFICE 2,052,318 ELECTRIC SWITCHING DEVICE Hnmphreys O. Siegmund,West Orange, N. 1., assignor to Bell Telephone Laboratories, In-

corporated, New York, N. Y., a corporation of New York Application May1, 1935, Serial No. 19,128

5 Claims.

tecting the contacts of electric switching devices against erosion suchas is caused at the contacts by sparks resulting from-the interruptionoftion energy in the form oi. a spark at the in-- terrupting contactscaused by an abnormal increase in voltage due to the opening of theinductive circuit. Such contact sparking causes a rapiddeterioration ofthe contact metal and renders the switching device less reliable inoperation.

Several expedients in the nature of spark suppressors, such ascondensers, filters, copper oxide rectifiers, and the like, have beenresorted to in an eilort to render the contact elements oi. switchingdevices immune to the deleterious eftests 01' sparking. .The use of suchremedial measures, however, requires a suitable mounting tor thesuppressor which, for the best results, should be located close .to thecontacts with which it is to function. It also necessitates wiring thesuppressor to the contacts or to the springs upon which the contacts aremounted which is usually accomplished after the switching device hasbeen installed. Such requirements are not always easily satisfied andare, therefore, objectionable.

It is the object of this invention to provide protection for the contactelements of a switching device in such a manner that the objectionablefeatures heretofore encountered are overcome.

This object is attained in accordance with a feature of the invention bythe use of a Thyrite resistance element as the spark suppressor and byincluding the suppressor as an integral part of the spring pile-up inwhich the contact bearing springs are assembled as a unit.

The invention will be readily understood from the following detaileddescription made with reference to the accompanying drawing, in which:

Fig. 1 is an exploded view of a simple spring pile-up, such as may beemployed in a relay, key

or other type of switching device and which illustrates the position ofthe suppressor element This invention relates to electric contactprotection and moreparticularly to means for prowith respect to thecontact springs with which it functions;

Fig. 2 is a characteristic curve illustrating the resistance voltagecharacteristic of Thyrite;

Fig. 3 is a circuit schematic showing the electrical connection of theThyrite resistance in a contact controlled circuit; and

Figs. 4 and 5 show practical applications of the present invention to anelectromagnetic switching device and a manually operated key,respectively.

In accordance with this invention, as illustrated by Fig. 1, the springpile-up consists primarily of a pair of cooperating contact bearingsprings l0 and II between which is interposed a block I2 01' Thyrite ofsuitable dimensions and drilled as shown, with holes which alignthemselves with corresponding holes in the springs and II for thereception of screws It. Insulating separators M and I5, also providedwith holes through which the screws l3 pass, complete the pile-upillustrated. The pile-up is assembled in the well-known manner, byplacing the various elements I, III, I2, H and I5 thereof, one on top ofthe other, with their respective holes in alignment and passing thescrews I! through the aligned holes and screwing them into the mountingbracket |6., The element l2 serves the dual purpose of a sparksuppressor and spring separator.-

The substance, Thyrite, has a non-linear resistance characteristic suchas illustrated by the curve in Fig. 2. It will be. noted from the curvethat the Thyrite has a substantially linear resistance at appliedvoltages below a certain value V but that when the applied voltageincreases to a value of V, the resistance ismaterially diminished. Thevoltage V may be considered to be the peak voltage of the inductivedischarge of the load L shown in Fig. 5 when the contacts I! are opened.The resistance of the element l2 being very low at this voltage, theenergy stored in the inductive load L finds a ready path to ground, saidpath being in shunt with the contact springs IO, N. The stored energyis, accordingly, dissipated without injury to the contacts I? and doesnot manifest itself in the form of a spark at these contacts.

The contact protector of this invention is simple, inexpensive andpracticable and occupies less mounting space than other arrangementsheretofore used for the same purpose.

Fig. 4 discloses an electromagnetic switching device, such as a rela andFig. 5 shows a manually operated key, in t e spring pile-ups or each ofwhich is included a 'i it. te hicch, such as 92, which functions in thenner just described to'protect the contact elements of the springsagainst the deleterious effects of spar.

What is claimed is:

1. In a switching device, a spring pile-up in= eluding a pair ofcooperating contact hearing springs and a separator interposedbetweensaid springs, said separator comprising an electrical conductor having anegative non-linear resistance-voltage characteristic.

2. In a switching device, a. spring pile-up comprising three contiguouselectrical conducting elements, one of said elements having a negativenon-linear resistance-voltage characteristic and located intermediatethe other two elements. j 3. In a switching device, a spring pile-upcomprising a pair of circuit controlling contact accents ing springs, aseparator having a. negative non linear resistance-voltagecharacteristic interposed between said contact springs, and means forsecuring said springs and separator to said switching device.

5. In a switching device, a pair of contact ring springs. a sparksuppressor interposed between said springs, and means for securing said15 springs and said suppresson'as a unit, to said device.

